Screw-thread-cutting tool for cutting tapered threads



Jan. "17, 1928. 1,656,593

J. D. MERRIFIELD SCREW THREAD CUTTING TOOL FOR CUTTING TAPERED THREADSFiled Feb. 19. 1925 Patented 17, 1928.

UNITED STATES 1,656,593 PATENT OFFICE.

JOHN D. MERRIFIELD, F ERIE, PENNSYLVANIA, ASSIGNOR TO REED MANUFACTUR-ING COMPANY, OF ERIE, PENNSYLVANIA "A CORPORATION OF PENNSYLVANIA.

SCREW-THREAD-CUTTING TOOII FOR CUTTING TAPERED THREADS.

Application filed February 19, 1923. Serial No. 619,879.

Screw thread cutting tools for cutting tapered threads as now ordinarilydesigned advance on the thread cutting both slopes ot the threads ascut. Ordinarily where H tapered threads are cut with a die the finishedthread is the thread under the die. In the present invention I provide acutting tool which is designed to cut tapered threads and to cut thethread from one slo e of the in thread. This has very material avantages in that it reduces the total line of severance and consequentlythe energy necessary to make the out. It forms a continuous or smoothwall on one slope without the steps M usually left b% the tool at pointswhere the cutterscease t eir forward movement. This is of materialimportance in cuttin pipe threads. It also forms ribbon-form c ips asdistinguished from the triangular-shaped ll chips and these can bereadily disposed of where the tail is backed off as a die, the out beingalong one wall and the chips of the fiat shape. There is no tendency forthe chips to jam, or retard the backing ofi of the die, nor is there antendency to injure the cut threads in t is operation. In carrying outthe invention where the cut is from one slope it is necessary to varythe pitch, or inclination of the s iral cut by the successive teeth tromthat o the finished thread in proportion to the thickness of the cut inone rotation of the die. Where the out is on the side in advance of thetrough of the thread it is necessary to make the lead enough faster thanthe lead of the finished thread to compensate for the thickness of thecut in one rotation of the tool so that the troughs will all be properlyplaced under the tool. In carrying out the invention I prefer to providethe die with starting teeth having one slope with an inclination varyingfrom that of the finished thread to facilitate the starting but with acrest formin a properly spaced trough in the finishe thread. Otherfeatures of the invention and details will appear from the specificationand claims.

The invention as exemplified is shown in the form of a die andillustrated as follows l i 1 shows an elevation of a chaser in aposition starting on a pipe.

Fig

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2 a similar view with the chaser further advanced.

Fig. 3 a view showing the completed cut.

at Fig. 4 a diagrammatical view showing the relation of the chaser teethto the teeth out on the die.

5 an enlarged view showing the successive cuts made in the progress ofthe die.

F i 6 a plan view of one of the chasers in position of the thread.

Fig. 7 shows a so-called solid die in which the chasers may be arranged.

1 marks the chaser, 2 the dierbod 3 a pipe or bar being cut. The chasersor ie has the finishing teeth 4 with the crests 4 and troughs 4 thestarting teeth 5 with the crests 5 and the troughs 5 and the fineentering teeth' 6 having the crests 6 and troughs 6". 'As shown in Fig.4 dash lines indicate the relation of the crests of the teeth with thetroughs of the teeth being cut.

The pipe ordinarily as out off has a burr l1 and the entering teeth 6are particularly designed to engage and pass this obstruction. Thestarting teeth form a small spiral groove 12 in the bar, leaving a flatcrest 13. This is the reverse of the ordinary manner of cuttings threadswith dies in that ordinarily the entering or starting teeth out a flattrough and leave hair-like threads on the bar. The difiiculty with thismethod is that these threads have not suificient substance to sustainthe thrust of leading on the die and consequently are stripped. With thepresent structure with the broad metal between the starting groovesthere is suificient metal to prevent stripping and it is consequentlpossible to start the die without the or inary lead screw.

The threads cut on the pipe have the crests 14, troughs 15, the forwardslope 16 and rearward slope 17.

The successive cuts are shown in Fig. 5, the entering teeth making a cutof material indicated at 18, the starting teeth .making cuts indicatedat 19 and the teeth a series of ribbon-like cuts as indicated at 20.

I prefer to set the chasers diagonally in that this gives a greater siderake to the cut and the biting in of the cutting edge tends to correctthe lag in the lead which occurs where the chaser is set more nearly inline with the axis. I

It will be observed as indicated by lines a that the troughs of theteeth in the die correspond with the peaks of the finished thread andinasmuch as the cutting is done entirely of the teeth in the cutter isas much greater the same lead as the other threads.

than the lead of the threads being cut. as the thickness of the cut inone rotation so that the troughs of the thread out are properly spacedunder the die. The lines I) extend from each tooth of the die to a toothcut at the inclination of the slope; 0-0 a line parallel to the axis andextending from the peak of the tooth of the die having the smallestradius; (2 the intersections of lines a and b and e intersections oflines a and b. The intersections at a of the lines a and the lines 6indicate the lead of the thread of the chaser. It will be noted that thedistances between the points 6 vary from the distances between the crestof the thread of the die and this indicates the thickness of the cut.Thus the variation in pitch which the cutting from one slope alone wouldbring about is rectified so that the troughs of all the finished threadsare properly spaced from the deepest cut to the most shallow cut. Iprefer to make the entering threads finer b(1)1t doif r narily there aretwo threads in the same space as occupied by one thread of the ordinarycutting thread and I prefer to make the starting threads with thecutting face inclined to the finished thread so that it will morereadily wedge on to the pipe and thus facilitate the starting of the dieon the pipe. This is done while still maintaining the troughs betweenthe threads in proper relation.

What I claim as new is 1. A screwthread cutting tool having taperedcutting teeth with crests spaced as the crests of the thread to be cutand with the pitch spiral along the slopes of the teeth whereby the cutof the tool is along one slope of the thread cut.

2. A screw thread cutting tool having tapered cutting teeth with theircrests spaced as thecrests of the thread to be cut, said teeth having apitch lead varying from the pitch of the thread to be cut whereb the cutis made on one slope of the threa 3. A screw thread cuttin tool forcutting tapered threads having teet in tapered relation and spaced asthe thread cut and spiraled and shaped to make their cuts on one slopeof the thread cut, the teeth at the starting.

end of the tool having one slope incline difierently than the succeedingt reads.

4:. A screw thread cuttin tool for cutting tapered threads having teethin tapered relation and spaced as the thread cut and spiraled and shapedto make their cuts on one slope of the thread cut, the teeth at thestarting end of the tool having their front slope inclined less abruptlythan the succeeding threads.

5. A screw thread cuttin die for cutting tapered threads having teet intapered relation and spaced as the thread cut and spiraled and shaped tomake their cuts on one slope of the thread cut, the teeth at the startin end of the die having one slope inclined di erently than thesucceedin threads.

6. A screw thread cutting is for cutting tapered threads having teeth intapered relation and spaced as the thread cut and spiraled and shaped tomake their cuts on one slope of the thread cut, the teeth at thestarting end of the tool having their front slope inclined less abruptlythan the succeeding threads.

7 A screw thread cutting tool for cutting tapered threads having teethin tapered relation and spaced as the thread cut and spiraled and shapedto make their cuts on one slope of the thread cut, the teeth at thestart ing end of the tool having one slope inclined differently than thesucceeding threads and having the crests of such threads similarlyspaced with relation to the crests of the succeeding teeth and spacedsimilarly to the troughs of the threads cut.

8. A screw thread cutting die for cutting tapered threads having teethin tapered relation and spaced as the thread cut and spiraled and shapedto make their cuts on one slope of the thread cut, the teeth at thestart ing end of the die having one slo e inclined differently than thesucceeding t reads and having the crests of such threads similarly spacewith relation to the crests of the succeeding teeth and spaced similarlyto the troughs of the threads cut.

9. A screw cutting tool having tapered screw cutting teeth having theircrests s aced as the crests of the thread to becut an having taperedstarting teeth finer, closer together and of the same lead as the screwcutting teeth.

-10. A screw thread cutting tool for cuttin tapered threads havin threadcutting teeth in tapered relation and spaced as the thread cut andspiraled and shaped to make their cuts on one slo e of the thread; andpointed starting teeth in advance of the thread cutting teeth finer butof the same pitch as the thread cutting teeth, said starting teeth beingin'the form of plural threads, certain of said threads being 1ncontinuation of the spiral of the thread cutting teeth.

11. A screw thread cutting tool for cutting tapered threads havingthread cutting their cuts on one slope of the'thread out, form of pluralteeth and certain of said intermediate teeth in advance of the threadteeth being in continuation of the spiral of cuttin teeth having oneslope inclined difthe thread cutt' teeth.

ferent y from the opposite slo e,and pointed In testimony w ereof I havehereunto set 5 starting teeth in advance of t e intermediate my hand,

teeth finer but of the same pitch as the thread cutting teeth, saidteeth being in the J D. MEBRIFIELD.

